use JWT timestamp to validate claims

[lutangar]

This allows better testability.

This feature is better described in the JWT class :

Allow the current timestamp to be specified. Useful for fixing a value within unit testing. https://github.com/firebase/php-jwt/blob/3b454f90f147db65a615041dec6661f427d6cb00/src/JWT.php#L43-L50

[lutangar]

Didn't notice at first but #178 is related. I could implement the JWT::$leeway in this one if interested.

[elernonelma]

Yes make sens 👍

[lutangar]

Added JWT::$leeway usage in 2b563b8, as seen in #178

This allows time manipulation for testing purpose. See JWTTest.php#L79-L90 for a usecase.

[lutangar]

Ping @hajekj